Biodegradation mechanism of asphalt by microbial consortia in asphalt pavement of forest area road

Abstract

To study the degradation behaviors of asphalt by microorganisms and reveal biodegradation mechanism of asphalt, 16S rRNA full-length sequencing was utilized to analyze the collected samples from three forest areas. Five strains, namely Sphingomonas polyaromaticivorans, Pseudomonas putida, Pseudomonas fluorescens, Bacillus cereus, and Bacillus subtilis, were selected for compounding microbial consortium to study its degradation effects on asphalt. The micromorphology, elemental chemical states, micromechanical properties, molecular weight distribution, and functional groups of degraded asphalt were studied using environmental scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, gel permeation chromatography, and Fourier transform infrared spectroscopy. The results show that the biodegradation of asphalt by microbial consortium increases the surface roughness of asphalt and reduces surface adhesion. Asphalt is used as the sole carbon source by microbial consortium, resulting in a continuous decrease in the contents of C and N elements, while the content of O element is continuously increased. Simultaneously, under the action of microbial enzymes, C-C/C-H bonds which are combined with molecular oxygen in asphalt are continuously broken and converted to C-O-C/C-O-H bonds. The continuous reductions in methylene index and butadiene index of asphalt, as well as the production of carbonyl functional groups confirm the oxidative degradation of asphalt by microbial consortium. Additionally, with the extension of degradation time, the large molecular substances in asphalt are gradually degraded by microbial consortium, leading to a more concentrated molecular weight distribution. This study is of great importance to understand biodegradation mechanism of asphalt.